The equating of scores on alternate forms of different achievement tests through the use of the three-parameter latent trait model, item-response theory (IRT) equating, was compared with the results of score equatings based on conventional linear and curvilinear equating models. Ten equatings were completed for pairs of alternate forms of the Advanced Placement Program, which measures different content areas and traits in each subject area. It was found that despite the apparent violation of the unidimensionality assumption, the equating results obtained through the IRT equating model were found to be in agreement with those of the conventional equating models. By demonstrating that the IRT equating results parallel those of the simpler, less costly, conventional methods, it has been shown that it is still possible to equate scores on non-parallel tests under conditions which make conventional equating inapplicable. (Author/PN)